Suspension devices have two main functions which have to be performed simultaneously at all times during operation. One of these functions is that of suspending the vehicle, that is to say of allowing each wheel substantially vertical oscillations. The other function of these devices is to guide the wheel, that is to say to control the angular position of the wheel plane.
The “wheel plane” is the name given to the plane, associated with the wheel, which is perpendicular to the axis of the wheel and which passes through the centre of the area of static contact with the ground when the wheel is vertical. The wheel plane thus defined is therefore firmly tied to the wheel axis and its orientation varies with that of the wheel.
The angular position of the wheel plane with respect to the body of the vehicle is defined by two angles: the camber angle and the steering angle. The camber angle of a wheel is the angle which, in a transverse plane perpendicular to the ground, separates the wheel plane from the mid-plane of the vehicle.
The steering angle of a wheel is the angle which, in a horizontal plane parallel to the ground, separates the wheel plane from the mid-plane of the vehicle.
The camber plane can be defined as the plane orthogonal to the ground, transverse to the vehicle and which passes through the centre of the area of contact of the wheel with the ground. This is the plane in which the camber movement takes place.
Patent application EP 1070609 describes a suspension device that allows the wheel a degree of freedom in terms of camber that is substantially independent of the suspension movements. The suspension movements are permitted by means of a multiple-link or double-wishbone system. The variations in camber are brought about by movements of the points of articulation of the link arms with respect to the body of the vehicle.
International application WO 01/72572 describes a suspension device in which it is the wheel support that gives the wheel a degree of freedom in terms of camber with respect to the suspension elements. This degree of freedom is controlled either actively, for example by an actuator on the basis of vehicle driving parameters, or passively through the forces exerted on the wheel in the contact area.
International application WO 04/058521 describes another wheel support device allowing the wheel a degree of freedom in terms of camber with respect to the suspension elements. The camber means comprise a triple hinge connected, on the one hand, to the wheel carrier and, on the other hand, to the suspension elements, the said triple hinge comprising two cheeks and two levers, each of the levers being secured to a respective one of the two cheeks, the levers being connected, on the one hand, to the wheel carrier and, on the other hand, to the suspension elements.
In the support and suspension devices described in the abovementioned patent applications there has been added, with respect to conventional suspension devices, a degree of freedom so as to allow the wheel some camber movement with respect to the body. This additional mobility may be afforded in various different ways but it is always the case that increasing the number of parts and the number of ball or pivot joints has a tendency to downgrade the rigidity and/or the robustness of the system as a whole. These systems are also relatively costly. What is more, the volume occupied by the suspension systems in motor vehicles is constantly being reevaluated in order to make more space for the passenger compartment or the wheels.